SPI hangs within RTC CC callback

[Steve H]

Hi all,

I'm transferring data to and from an Atmel AT25040 NVRAM using SPI, and it works perfectly when run within main(). However, if I run the same code from within an RTC CC callback, the blocking call to nrf_drv_spi_transfer() never returns.

Any suggestions gratefully received!

[MartinBL]

Hi,

What kind of interrupt priorities do you use? If you are calling a blocking function from within an interrupt it might be that the SPI transfer is waiting for the RTC interrupt to complete. However, this will never happen if you use a blocking nrf_drv_spi_transfer() from within the RTC interrupt itself, because even a blocking nrf_drv_spi_transfer() is waiting for an SPI interrupt, only behind the scenes deep down in the drivers. If you haven't done so already, can you try to increase the interrupt priority of the SPI driver, to something higher than the RTC interrupt? You can do it in sdk_config.h.

[Steve H]

Thanks, Martin, that seemed to fix it. Are there better ways of implementing this scenario?

[MartinBL]

Either you need different priorities, or you can set a flag in your RTC interrupt, check this flag in your main loop, and then transmit when the flag is set.

[Steve H]

Thanks again, I'll look again at my code but it seems to be working OK.